Apparatus for reproducing video tape recordings in slow motion



March 31, 1970 J. L. E. BALDWIN 3,504,119

APPARATUS FOR REPRODUCING VIDEO TAPE RECORDINGS IN SLOW MOTION FiledSept. 8, 1966, Y 7 Sheets-Sheet i FIGS INVENTOR. JOHN L. E. BALDWINAGENT March 31, 1970 1 B wm 3,504,119

APPARATUS FOR REPRODUCING VIDEO TAPE RECORDINGS IN SLOW MOTION FiledSept. 8, 1966 '7 Sheets-Sheet 2 FlG.3a

FIGAa '=-T26-1o"rn*- INVENTOR.

Y JOHN LE. BALDWIN AGENT March 31, 1970 J. L. E. BALDWIN ,1

APPARATUS FOR REPRODUCING VIDEO TAPE RECORDINGS IN SLOW MOTION 7Sheets-Sheet 5 Filed Sept. 8, 1966 FIG.2

AGENT March 31, 1970 J. L. E. BALDWIN 7 3,504,119

APPARATUS FOR REPRODUCING VIDEO TAPE RECORDINGS IN SLOW MOTION FiledSept. 8, 1966 7 Sheets-Sheet 4.

FIGBc I N VE N TOR.

JOHN L. E. BALDWIN wzLf AGENT March 31, 1970 J. L. E. BALDWIN ,1

APPARATUS FOR REPRQDUCING V IDEO TAPE RECORDINGS IN SLOW MOTION 7Sheets-Sheet 5 Filed .Sept. 8. 1966 F I G.6d

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23456 009 mA BWWwBN INVENTOR. JOHN L. E. BALDWIN BY MK AGENT March 31,1970 J. L. E. BALDWIN APPARATUS FOR REPRODUCING VIDEO TA'PE RECORDINGSIN SLOW MOTION 7 Sheets-Sheet 6 Filed Sept. 8. 1966 u N 1P |F.k| 11? k.IF q s I n 4 0 N w 2 0 INVENTOR JOHN L.E.BALDWM AGENT March 31, 1970 J.L. E. BALDWIN- APPARATUS FOR REPROUUCING VIDEO TAPE RECORDINGS IN SLOWMOTION Filed Sept. 8, 196G 7 Sheets-Sheet 7 FIGS FIGJO INVENTOR. JOHNLE. BALDWIN AGENT United States Patent 3 504,119 APPARATUS FORREPRODUCING VIDEO TAPE RECORDINGS IN SLOW MOTION John Lewis EdwardBaldwin, Croydon, England, assignor, by mesne assignments, to US.Philips Corporation, New York, N.Y., a corporation of Delaware FiledSept. 8, 1966, Ser. No. 578,065 Claims priority, application GreatBritain, Sept. 10, 1965, 38,854/ 65 Int. Cl. H04n 1/28, 1/24 U.S. Cl.1786.6 7 Claims ABSTRACT OF THE DISCLOSURE Video tape reproducingapparatus for producing slow motion pictures from recorded video tapeusing an assembly of n reproducing heads staggered along a helical pathor a rotor having a larger diameter than the recording rotor, where thetape passes over the rotor at an angle depending on the ratio of theangular speeds of rotation of the recording and reproducing rotors.

The invention relates to apparatus for reproducing video taperecordings. More particularly, the invention relates to reproduction atslow speed with apparatus and recordings especially (though notexclusively) of the helical type wherein each track contains one field.

There is a requirement for a device which will accept normal televisionpictures and reproduce them at a reduced speed so providing slow motion.Slow motion using film is a well-known technique for'the analysis ofmovement and in trick photography to alter the apparent size of objectsbeing affected by the force of gravity.

Any device producing slow motion must, by definition, inevitably storeinformation.

The magnetic recording of television signals is now standard practiceand for monochrome use is now approaching perfection. The provision ofslow motion has, however, been neglected with a few exceptions. Thefirst was by the American Broadcasting Company in conjunction withAmpex. The principle used was to slow the whole operation of themagnetic reproducing equipment down to either a half or a quarter speedand to reproduce the picture on a special monitor capable of operatingat 525 lines, 15 or 7 /2 frames per second. A camera operating at 525lines, 30 frames per second converted the picture on the monitor to thenormal U.S.A. television standards. The results were not satisfactory;smearing and flicker were apparent at half speed and at a quarter speedthe flicker was intolerable.

In 1964, N.H.K. of Japan produced some equipment used at the OlympicGames. Results were satisfactory, but the price was 100,000. Some otherJapanese equipment has been made selling for about 5 0,000.

The work done so far has been based on quadruplex machines although thesecond Japanese machine used a helical recorder as an intermediatestore.

The problem of providing slow motion will now be described withreference to FIGURE 6 of the accompanying diagrammatic drawings asapplied to helical recorders.

It would appear at first sight that all that is needed to obtain slowmotion from a helical recorder is to decrease the speed of the tapethrough the machine.

Certainly slowmotion is produced but with it come many defects most ofwhich are attributable to the change in tape speed.

The magnitude of these defects will vary slightly from one design ofrecorder to another but the figures given for the Philips EL3400A may beconsidered typical. For this particular recorder operating on the 625line TV 3,504,119 Patented Mar. 31, 1970 ice Standard, the movement ofthe head during one field is 310 line pitches while the normal movementof the tape (referred to as K) during the same interval is in thisexample 2 /2 line pitches yielding the desired total of 312 /2 lines (Kis also the field pitch cfr. FIGURE 6C). To take a hypothetical case:

Replay on same machine at /5 normal speed. The tape now moves only halfof a line pitch per field.

Errors:

(1) The average number of lines per field is 310 /2 and not 312 /2. Thisis not admissible.

(2) The number of lines per field varies. In four out of five scans itis 310 lines and at the fifth it is 312 /2.

(3) Line frequency incorrect assuming mean field frequency is correct(i.e., 310 /2 lines instead of 312 /2 (4) Field frequency modulated at10 c./s. causing a vertical hopping of the picture (cfr. FIGURE 6C:e.g., there is a sudden jump in sync. timing from the 5th scan (a) oftrack t1 to the first scan (18) of track 1 and so forth.

(5) Interlace seriously upset.

(6) Tracking impossible for uniform tape and head motion because thetracking angle is wrong and there is displacement normal to the track(cfr. FIGURE 6B).

This is obviously not suitable. It is possible to cure errors 1, 3 andto some extent 6 by using a slightly different replay machine, but othererrors remain to be considered.

FIGURE 6A shows that the angle 61' at which a track was recorded acrossthe tape (with tape helix angle 0t) is dependent on the circumference ofthe drum and the relationship between head motion (AC) and tape motion(BC) giving a track AB at said track angle 6r. If the speed of the tapeis reduced by a factor of 5:1 (so that B only moves to B) to obtain slowmotion playback then the head motion (and the circumference of. thedrum) is wrong and the readout head does not traverse the tape at thesame angle as the recorded track.

It is an object of the invention to overcome these difficulties.

According to its broadest aspect the invention provides video tapereproducing apparatus for producing video signals for a slow motionpicture from a tape recorded at normal speed (as defined) whichapparatus comprises:

(a) Means for transporting tape at a constant speed which is a fractionl/n of the original recording speed, n being an integer;

(b) Means for scanning n times in succession the recording whichrepresents a given field;

(c) Means for causing the scans to track (as defined) the recording inspite of the change in tape speed;

((1) Means for causing the timing of successive field scans to be suchthat corresponding video information is scanned at substantially equalintervals of time.

The term normal speed refers to the original speed at which the tape wasrecorded. The term to track means broadly that a head of finite andpracticable gap width can remain within the width of the recorded trackduring the whole of a scan running preferably (though not necessarily)parallel thereto.

Before describing actual embodiments of the invention it is desirable todescribe partial applications of the invention as separate steps whichhave to be combined in a complementary manner.

First, with reference to feature (c), it will be seen from FIG. 6b thatthe tape helix angle at of the conventional recording arrangement can bechanged to a value 0t where the final position of point B of the tapewill be at the slit or scan path SS (as desired) at the end of the scanperiod. This is done by rotating the tape round point A to a new (slowmotion) tape position where B lies on 6 line SS (point B is the positionreached by element B of the tape due to tape motion at the 5:1 reducedspeed, as was explained with reference to FIG. 6a).

This still leaves a discrepancy between the original head scan motion ACand the new (desired) head motion AB. The head motion can be lengthenedto the desired value AB by increasing the diameter of the head rotor anddrum (with our previous assumptions this increase in rotor circumferencewill be in the ratio 312/310).

The errors of the previous hypothetical case that have been removed bythis partial application of the invention are:

(1) The average number of lines per field is no longer 310 /2 but is now312 /2 as desired.

(2) Both line and mean field frequency can be correct at the same time.

(3) The tape helix angle 01 is now correct but only one of the fivescans (S3, FIG. 6d) can be made to track perfectly for a whole field.Two of the remainder (S2 and S4) will be so close as to be admissible.The remaining two (S1 and S5) will be problematical but may be madetolerable by decreasing the reproducing head track width to 90 for arecording head of 120p.

Errors remaining: 1

(1) The number of lines per field varies. It can be shown that in fourout of five scans it is 312 lines, in the fifth scan it is 314 /2.

(2) Field frequency modulated at 10 c./s. causing a vertical hopping ofthe picture.

( 3) Interlace seriously upset.

(4) Tracking displaced laterally in scans Sl-S2, S4, S5 though angle iscorrected (FIG. 6d).

By applying a further feature of the invention these lateraldisplacements of tracks can be overcome by using scanning means whichcomprise a plurality n of heads which are rotatable together and arestaggered along the axis of rotation, the stagger being obtained bydisposing the heads substantially at equal distances along a singlestartor multi-start helix, which in effect means disposing them approximatelyat equal arcs round the head rotor periphery with transverse (i.e.axial) stagger displacements substantially equal to a fraction 1/ n ofthe recorded track width.

The stagger of the heads permits, for example, the center lines S1 to S5of the five scans of FIG. 6d to be coincident. If they are also parallelto the tracks 2, (t+1) etc. due to other aforesaid features of theinvention then the playback head may be substantially as wide as therecorded track.

For apparatus adapted for use with tape recorded on a helical machine ofthe type in which the tape passes round a cylindrical drum on a helicalpath and the resulting tape is such that each track corresponds to onefield, the reproducing apparatus may have a scanning rotor of suchdiameter that each head traverses an effective scanning arc (as defined)which is longer than the effective scanning arcs used for the originalrecording to an extent such as to compensate for some of the aboveerrors due to the nzl reduction in tape speed (cfr. FIG. 6b).

The effective scanning arc is the arc which is traversed by a headbetween the instant when it is switched on by the circuitry of theapparatus and the instant when it is switched 011.

The reduction in speed is preferably done by an odd ratio (e.g. 3:1 or5:1) rather than by an even ratio (e.g. 4:1) for reasons which willappear below. The ratio 5 :1 adopted in the examples has the addedadvantage of giving the slowest speed which can generally be adoptedwithout destroying the illusion of motion (with a SO-field-per-secndinterlaced standard the :1 ratio gives 10 picture changes per second;similarly, a 60-field standard gives 12 picture changes per second).

In the case of slow-motion playback apparatus according to the inventionhaving increased effective scanning arcs as aforesaid, the playbackapparatus itself is preferably of the helical type in which case onepreferred form has the following characteristics:

(a) It is adapted for use with tape based on interlaced fields eachcontaining x+ /i lines where x is an integer;

(b) It employs n (where n is an odd number) scanning heads adapted torotate at such speed that each head scans one track in one field period,the heads being employed in the order 1, 2, 3 n;

(c) The arcs of separation (as defined) between successiveiy used headsalternate between x and (x+1) lines except between heads n and l wheresaid spacing is (x+ /2 :K) lines where K is the displacement (asdefined) between field pulses of successive recorded tracks expressed inlines, this quantity K being an odd number of half lines;

(d) The pitch of the helix described by passage of the tape over thedrum is related to that used originally in recording the tape in thatthe slow-motion helix pitch is given by the original tape helix pitch ofa single-head recording machine multiplied by the ratio of the angularspeed of rotation of said single-head recorder to that of theslow-motion rot-or.

The said ratiois almost exactly equal to the ratio of the playback drumdiameter to the single-head recording drum diameter. (If the tape usedhad been recorded e.g. on a two-head machine with a drum of twice thediameter, suitable allowance must, of course, be made in thecalculation.)

The arcs of separation are the arcs which are measured between one headand the next one to be used and represent the geometry of thedisposition of the heads on a rotor. These arcs are of similar lengthto, and may or may not be exactly the same as, the correspondingeffective scanning arcs depending on circumstances.

Alternatives to the small differences in the lengths of arc in this lastarrangement can be used (e.g. delay iines, as will be explained later)but first some examples of such an arrangement, taken as preferredembodiments of the invention, will now be described by way of examplewith reference to the accompanying drawings as applied to 5:1 speedreductions in an interlaced system using helical machines and helicalrecordings.

In the drawings:

FIGURE 1 shows an arrangement in which the head rotor and drum areincreased approximately 5 times in circumference.

FIGURES 2 to 4 show arrangements in which the arcs of separation(between consecutively used heads) overlap so as to reduce the diameterof the rotor and drum. In particular:

FIGURE 2 has the five heads arranged in sequence 1, 4, g, 5, 1, 4, 2, 5,3; 1 and used in the order underlined, the speed of rotation inrevolutions per second is equal to F where F is the field frequency, andthe circumference of the drum equals arcs of separation.

FIGURE 3 has the five heads arranged in sequence 1, 3, 5, g, 4, l, g, 5,2, g, 1, 3, 5, 2, 4, l and used in the order underlined, the speed ofrotation in revolutions per second is equal to F /s where F is the fieldfrequency and the circumference of the drum equals arcs of separation.

FIGURE 4 has the five heads arranged in sequence 1 5, 4, 3, g; 1, 5, 4,g, 2; 1, 5, g, 3, 2; 1, i, 4, 3, 2; l, and used in the order underlinedthe speed of rotation in revolutions per second is equal to F /s where-F is the field frequency, and the circumference of the drum equals 7arcs of separation.

FIGURE 5 shows a modification of the arrangements of FIGURES 1 to 4wherein all the heads are almost at the same position on the drumperiphery.

FIGURES 1A to 4A show rotor developments indicating the particularstaggered arrangement of the heads of FIGURES l to 4 respectively.

FIGURES 5A-5B show similar developments for the arrangement of FIGURE 5,FIGURE 5A being theoretical while FIGURE B is possible though difiicultto achieve with present technology.

FIGURES 6A to 6D are diagrams which have already been used in thepreliminary explanations.

FIGURE 7 shows a simplified interlaced raster with an elementary form ofmodulation.

FIGURES 8a-8d show schematic video waveforms related to said raster.

FIGURE 9 shows a head-switching circuit employing delay lines to achieveinterpolation of field information.

FIGURE 10 shows a head-switching circuit employing delay lines toreplace the small differences in the arcs between the heads of FIGURES 1to 4.

The standard assumed (for convenience) is the 625- line standard.

In FIGURES 1 to 4 inclusive the heads are substantially evenly spacedabout the circumference of the drum while in FIGURE 5 they are veryclose together or approximately at a common position. There are manysimilarities in the solutions of FIGURES 2 to 4 and these will betreated together.

Some specific comments should be made on the constructions of FIGURES 1to 5.

FIGURE 1:

There is the problem of the size of the drum which has to be 755 mm. indiameter. Switching from the output of one head to the next can readilybe done by known circuit means. The tape should be wrapped round thedrum to an extent somewhat greater than about 72 (as shown) owing to thestagger of the heads though it could be wrapped right round the drum ona conventional helical path if desired.

In the present example the arc of separation between heads 5 and 1 is310 lines because the field pitch K has been assumed to be 2 /2 linesand the direction of movement of the heads is opposite the direction ofmovement of the tape. Should the latter not be the case the said arc ofseparation is 315 lines.

The one physical parameter which is not defined in the drawing is thepitch of the tape helix, i.e. the helix which the tape would define ifit were wrapped once right round the drum instead of embracing onlyabout /5 of the drum. As defined previously, this pitch is obtained bytaking the original tape helix pitch of a corresponding single-headrecorder (diameter 150 mm.) and multiplying it by 5. The value 5 can betaken as the ratio of re cording rotor angular speed to playback rotorangular speed or it can be taken as a nominal increase in the drumcircumference (this nominal increase in the drum has been made to differslightly from the actual increase so as to obtain correct trackingangle).

As shown in FIGURE 1A, the centers of the heads 1-5 are staggeredtransversely by /s of track pitch a (for example 36p. with a gap widthof 120-150,u) and lie on a single-start helix.

FIGURES 2-4 inclusive:

In these cases the drum diameter has a more convenient size. Since,again, the tape need not be wrapped completely round the drum theproblem of connecting the two component parts of the drum is easilysolved. Head switching requires more complicated circuitry than FIG-URE 1. Since the head wheel rotates 2, 3 or 4 revolutions in 5 fields,the generation of five impulses per revolution together with a countercircuit provides a method of stabilizing and controlling the speed ofrotation. It may also be necessary to consider ambiguity of position.The probable choice is the arrangement of FIGURE 4 unless the size ofthe drum is regarded as too small for the five pre-- amplifiers andswitching circuits.

In a manner analogous to FIGURE 1, the pitch of the tape helix isrelated to the original single-head recording helix by the factor(FIGURE 2) or (FIGURE 3) or (FIGURE 4).

As shown in FIGURES 2A-3A-4A the head centers are staggered e.g. by 36p;in 2 of these cases they lie on multi-start helices.

FIGURE 5:

This modification of the invention is in many ways the most interesting.It has some distinct advantages over the other solutions but it also hasits own problems.

The major problems are that heads 1 and 2 (and also 3 and 4) have topartially occupy the same space (cfr. FIG. 5a). With a track width of120150 mm. the lateral displacement between centers of adjacent heads isonly 36 m. It is possible to turn this to advantage by using onereproducing head with a width of ,um. to perform the functions of bothheads 1 and 2 (head A of FIGURE 5B). Another such head (head B of FIGURES'B) can perform the functions of heads 3 and 4. A third head (C) willthen be required as head 5. This cuts down the number of heads from fiveto three and also cuts down the number of pre-amplifiers and switches.During the second pass of head A, head B will be producing the samesignal delayed by one line and similarly, at the second pass of head B,head C will be producing a signal delayed one line from that of head B.This is because the 3 heads are spaced apart (peripherally) by 1 lineover a distance 1, as shown. The circumference of the drum is 312 lines.

The arcuate separation of the head gaps (which is approximately 1.5 mm.)has to be held to a tolerance of about 5 1.. This error needs aswitchable delay line of 0.2 s. for compensation. The requiredtheoretical accuracy is about 0.03 ,uS. The lateral displacement fromone head to the next should be about 60,11. in this case. The trackingerrors in ,u produced due to this geometry are as follows:

HEADS The errors are insignificant when one head is used along butbecome significant (though small) when two heads are in use (e.g. forinterpolation as explained later). Under these latter conditions beatscan be reduced by 6 db and noise by 3 db due to the fact that each headproduces only half the output signal. A great advantage of thearrangement of FIGURE 5 is that the head wheel rotates once per fieldwhich considerably simplifies the head Wheel servo system.

To sum up the geometry of FIGURES 1 to 5, the arcs of separation of theheads are tabulated for convenience and are common to all FIGURES 1-5:

Separation head 1-head 2-3 12 lines Separation head 2-head 3-313 linesSeparation head 3-head 43 12 lines Separation head 4-head 5313 linesSeparation head 5-head 1310 lines (312.5 2.5

The sum of all these arcs is 1560 lines.

Before embarking on the further description it is desirable to restatecertain requirements of the present system which are:

(a) To be able to repeat a field a desired number of times (n) and thenchange to repeating the next field in sequence the same desired numberof times and to carry on this process as long as is likely to berequired.

(b) To enable the picture to comply with the normal television standardsit is necessary to be able to change an odd field into an even field orvice versa whenever required.

This later requirement could have been obviated by repeating framesrather than fields but where there is rapid movement (and there islittle likelihood of a demand for slow motion if the original movementis not rapid) repeated frames produce a double image of the subject orits background, whereas repeated fields produce a much smoother effect.

Changes from odd to even can be efiected as follows. The information ona particular line of one field is very assumption and it gives thewaveform shown in FIG. 8c, in which F indicates the required field pulseposition.

At this point it may be worth summing up the operation of thearrangements described.

Maintaining the assumption that the head and tape similar to theadjacent lines on the next field, i.e. the line move in oppositedirections, which as such is not necesabove and the line below. Thetiming of these lines is half sary, the common part of all solutions isa first head scana line before or half a line later. If on alternatefields ning a track and, when it has effectively passed 312 lines weadvance the picture in time by half a line period, the of information, asecond head starts scanning the same information on the picture islifted by one raster line. 10 track. During the second head scan we caneither tolerate Vertical lines in the picture are not adversely affectedbut the picture information jumping up one line or we can horizontallines jump up and down at frame rate. This is use a one-line delay topermit an interpolation of picture objectionable. The same thing happensif the repeated information.

field is delayed by half a line period when we wish to After the secondhead has effectively passed 313 lines change the type of field, the onlydifference being that in of information a third head starts its scan andin turn, this case the picture drops by one raster line. This disadafter312 lines have been effectively traversed, a fourlh vantage may beavoided by using neither a half line adhead comes into operation. Thesignal from the fourth vance nor a half line delay but th m an f bothighead is treated in the same way as that from the second nals. This maybe made more obvious by considering two head. Again, as in the case ofthe second head, after 313 adjacent lines on one field, say lines 99 and101. On the lines of information have been etfectively passed a fifthneXt fi ld f r line 100 We could se l n 101 y P head comes intooperation scanning this track for the last ing a half-line advance or wecould use line 99 using a i half line delay but the correct solutionwould obviously After the fifth head has effectively Scanned 3121/2 P tol an equal e of the Smee lme 100 hes lines, the first head is at thecorrect point to begin its lmmefhatily between hues 99 and scan of thenext track in sequence. Since the informa- Thls W111 be undeiflstood iclearly from FIGURES tion on this track is displaced by 2 /2 lines(factor K) fia l i efor dir ig 1522132?gsg iiig tggi g g j gfi ffig thearc of separation between head 5 and head 1 is that the displacementbetween tracks is 2 /2 lines and a only 310 hnes' Should the elreellonof movement of g 21-line picture as shown in FIGURE 7 is to be reducedin heads e the Same as the dleeetlen of movement of t e speed by 5:1.The picture includes for convenience a tape thls'last f of Separatlon315 lmesgraded bright horizontal bar extending right across and Theemphasls has been on an odd P ofrepetl' represented b vertical d l i Myli 4 15 tions of one field. A further reason for th1s is that, not and5) and a thin bright vertical bar extending from top 3 does one have tochange a $ma11e1 Percentage f to bottom and represented by horizontalmodulation Mh, the fields from odd to even or vice versa, but the pat-The later bar is indicated as a spike in the graphs of FIG- tern of thischange is the same every time. For example, URE 8. if the slow motion is5 to 1 the pattern is'as follows:

Number of field 1 2 3 t 5 6 7 8 9 l0 d E en 0 e o e o e iliiffiiiiihiiijjiii:::::::: Sat Even Change required on fields X X XEvidently it is desirable that the output signal should In this caseonly the second and fourth of every five reclosely resemble that shownin FIG. 8a. If the repetitive peats have to be changed. scanning of thefirst (odd) field of FIGURE 8A by five Consideration will now be givento certain alternatives heads H -H is considered it would insteadprovide the to the arrangements of FIGURES 1 to 5. same modulation bothon the odd and the artificial even I may be desir ble (egfrom amanufacturing polnt lines (FIGURE 8B). In FIGURE 8 field pulses are notof view) to place the five heads equally spa ed shown because thenecessary displacement for interlace on the head wheel. If this Is donethe read-out will be requires the field synchronizing pulses to bereformed. In as s n 111 FIGURE 8D- other words, since it has beenarranged that the line in- It Will be seen that only heads 1 and g1ve1nforn 1aformation is continuous, the recorded field sync informan OutWhich is timed in the Way that IS desirable 1.e. tion must be removedand true interlaced field sync pulses as in FIGURE 8B. In order to bringthe other signals generated and inserted to give the desired alterationof to a suitable timing it is necessary to delay the s1gnal odd and evenfield from heads 3 and 4 by one line duration and that of It may be seenfrom FIGURE 8B that at all times the hea 5 by two lines duration.Thispcan be done by a read-out from heads 1, 3 and 5 (H H and H containsswitching circuit employing delay llnes DL and DL the desired pictureinformation, whereas the read-out from as hown in FIGURE 1t heads 2 and4 (H and H (whilst being correctly timed In delay 11I 1eS can be usjidfor P P as regards line information) contains field information toObtaln lntefpolatlon 0f field lflfomlatlol} e which is incorrect, thisbeing implicit in trying to convert scrlbed above (FIGURE to adlust thetlmlng of from even to odd fields or vice versa. A better approximat had signals When the angles between heads are equal tion to the desiredsignal can be obtained by taking the descrlbed above Wlth refficncfi 10FIGURE signals from h d 2 d 4 d processing h i th (c) to take out smallerrors due to mechanical tolerances f u i in head pos1t1on (e.g. a 9.2,tLS, ad ustable delay may be One-half of the signal is taken and mixedwith one-half PFOVlded in the Output cllcult of each h of the signalwhich has been delayed by one line thus e g e y be used In y m lnagivena signal which is interpolated in the vertical directlon deslred and arrg (FIGURE can be tion in the units AD. This can be done by a switching 7bi i the lrregular head are r nts f circuit which includes delay linesand attenuators and a FIGURES t head selecting switch S, e.g. as shownschematically in What 1s claimed is:

FIGURE 9. It assumes that information appearing on 1. Apparatus forproducing video signals for a slow line 15 is the average of thatappearing on lines 4 and 5. motion picture from a tape recorded atnormal speed Reference to FIGURE 7 shows this to be a reasonable on ahelical machine of a type wherein the tape passes before a rotatedrecording head around a cylindrical drum on a helical path, wherein eachtrack corresponds to one field, and wherein the video information isrecorded in interlaced fields each containing X /2 lines, where X is aninteger, comprising means for transporting the tape at a constant speed1/ n times the original recording speed, a scanning rotor, n reproducingheads disposed on said rotor at substantially equal distances along ahelical path, said rotor having a diameter such that each head traversesa longer eifective scanning are than the eifective scanning arcs used inthe original recording, means for rotating the heads and rotor at such aspeed that each head scans one track in one field period in the order 1,2, 3 n, the arcs of separation between successive scanning headsalternating between X and X+1 lines except between heads n and 1 wherethe spacing is X+ /2:K where K is the displacement between field pulsesof successive recorded tracks expressed in lines, wherein K is an oddnumber of half lines, and wherein the tape is passed over the rotor andreproducing heads at an angle equal to the corresponding angle of therecording apparatus multiplied by the ratio of the angular speed ofrotation of the recording head to the rotational speed of thereproducing rotor.

2. Apparatus as claimed in claim 1, wherein the arcs of separation arearranged to overlap.

3. Apparatus as claimed in claim 2, wherein n=5, the five heads beingarranged in the sequence 1, 4, g, 5, 33 1, g, 2, 5, 3; 1 and used in theorder underlined, wherein the speed of rotation in revolutions persecond is equal to F x /s where F is the field frequency, and whereinthe circumference of the drum equals arcs of separation.

4. Apparatus as claimed in claim 2, wherein the five heads are arrangedin the sequence 1' 3, 5, 2 4, l, g, 5, 2, 4, 1, 3, g, 2, 4, 1 and usedin the order underlined, wherein the speed of rotation in revolutionsper second is equal to F /s where F is the field frequency, and

wherein the circumference of the drum equals arcs of separation.

5. Apparatus as claimed in claim 2, wherein the five heads are arrangedin the sequence 1, 5, 4, 3, 2 l, 5, 4, 2; 1, 5, g, 3, 2; 1, 5, 4, 3, 2;1 and used in the order underlined, wherein the speed of rotation inrevolutions per second is equal to F /s where F is the field frequency,and wherein the circumference of the drum equals arcs of separation.

6. Apparatus as claimed in claim 1, wherein electri-cal delays areincluded in the circuits of appropriate heads to efiect interpolation ofthe video information when converting an even field into an odd field,or vice versa and wherein n is chosen to be an odd number'so that suchconversion of field type occurs always at the same heads.

7. Apparatus as claimed in claim 6 wherein n=5 and wherein theconversion occurs always at heads 2 and 4.

References Cited UNITED STATES PATENTS 3,359,365 12/ 1967 Kihara.3,095,473 6/ 1963 Roizen. 3,157,738 11/1964 Okamura. 3,168,618 2/ 1965Sondermeyer 3,229,035 1/1966 Bounsall. 3,375,331 3/1968 Okazaki.3,376,395 4/ 1968 Rumple. 3,395,248 7/ 1968 Suzuki.

ROBERT L. GRIFFIN, Primary Examiner JOSEPH A. ORSINO, JR., AssistantExaminer US. Cl. X.R. 179-1002

